1. Field of the Invention The present invention relates to a structure of an optical connector and an aligning method for obtaining coincidence between the optical axes of optical fibers to be coupled to each other.
2. Description of the Related Art Referring first to FIGS. 3 to 6, a description will be made hereinbelow of a structure of a prior optical connector assembly made by the present assignee of this application.
FIG. 3 is a cross-sectional view showing the optical connector assembly, FIG. 4 is an illustration useful for explaining a fitting structure of a tube base fixed to a ferrule body and an optical connector housing, FIG. 5A is a perspective view showing the optical connector housing cut vertically, FIG. 5B is a perspective view showing the tube base fixed to the ferrule body, and FIGS. 6A and 6B are perspective views showing the optical connector housing and a key.
As shown in FIG. 5B, a tube base 2 has a cylindrical configuration and a portion 2d of an inner diameter of a hollow section 2c is formed to have a dimension slightly smaller than an outer diameter of a ferrule body 1. Further, a plurality of notch portions 2a and a plurality of fitting portions 2b are formed on an outer circumferential portion of the tube base 2.
The ferrule body 1 is fitted in the aforesaid inner-diameter portion 2d under pressure.
The ferrule body 1 has, at its central portion, an elongated small hole 1a for accepting and holding an optical fiber, and a clad portion of the optical fiber is inserted into this small hole 1a and fixed through an adhesive thereonto.
As shown in FIG. 5A, the optical connector housing 3 has a hollow section 3c having an inner diameter larger than the outer diameter of the tube base 2 and further has, in its bottom surface, a through hole 3a larger than the outer diameter of the ferrule body 1. In addition, on an inner circumferential surface of the hollow section 3c, one or more projecting portions 3b to be fitted in the notch portions 2a made in the outer circumferential portion of the tube base 2 are formed connectively with the through hole 3a. Moreover, a screw thread 3e is made in an inner circumferential surface of the hollow section 3c. Further, as shown in FIG. 6B, a circumferential groove 3d is made in an outer circumferential portion of the optical connector housing 3, and a key 4 with a tongue portion 4a shown in FIG. 6A is fixedly fitted over the circumferential groove 3d.
A holder 6 to be screwed into the optical connector housing 3 has a hollow section 6a with an inner diameter larger than an outer diameter of an optical fiber sheath 11 and further has, at its end portion, a coupling hole 6d with an inner diameter larger than an outer diameter of a spring 5, with a step portion 6c being formed between the coupling hole 6d and the hollow section 6a. A screw thread 6e is made on an outer circumferential portion of the holder 6.
In assembling, the ferrule body 1 is inserted into the optical connector housing 3 in a direction indicated by an arrow 13 in FIG. 5B, and the notch portions 2a of the tube base 2, fixed to the ferrule body 1, are engaged with the projecting portions 3b formed on a case section bottom surface. Whereupon, as shown in FIG. 4, an optical fiber end surface 1b of the ferrule body 1 protrudes from the through hole 3a in the case section bottom surface to the exterior of the optical connector housing 3.
As shown in FIG. 3, over the outer circumferential portion of the tube base 2 there is fitted the spring 5 having an outer diameter smaller than an inner diameter of the coupling hole 6d of the holder 6. One end portion of the spring 5 is placed against rear end surfaces 2e of the projecting portions 2b of the tube base 2, and in a manner that the screw thread 3e of the optical connector housing 3 is engaged with the screw thread 6e of the holder 6, the other end portion of the spring 5 hits against the step portion 6c of the holder 6.
Furthermore, a housing cover 10 having a screw thread 10b in its inner circumferential portion is set on the optical connector housing 3, thereby completing the optical connector assembly.
Secondly, using an adapter housing, a description will be made hereinbelow of a coupling structure of the aforesaid optical connector assembly. FIG. 7A is a side elevational view showing an adapter housing, FIG. 7B is a cross-sectional view thereof, FIG. 8A is a perspective view showing the adapter housing vertically cut, FIG. 8B is a perspective view showing a sleeve, FIG. 9 is a front elevational view available for describing the coupling structure of the optical connector assembly based upon the adapter housing, and FIG. 10 is an illustration for describing a method of making the coincidence between the axes of end surfaces of ferrule bodies within the adapter housing.
As shown in FIGS. 7A, 7B, 8A and 8B, an adapter housing 8 has, at its both end portions, circular tube grooves 8a each accepting the tip portion of the optical connector housing 3 and further has coupling grooves 8b each accepting the tongue portion 4a of the key 4. Further, it has, on its outer circumferential portion, screws thread 8c each engaged with the housing cover 10. In addition, it accepts, in its interior, a cylindrical sleeve (made of a metal or a zirconia ceramic) 9 having a cut section 9a at its central portion.
For the connection of the optical connector assembly, as shown in FIG. 9, the ferrule bodies 1 of the optical connector assemblies are respectively inserted from both sides into the adapter housing 8. The ferrule body 1 enters the sleeve 9, and the tongue portion 4a of the key 4 is fitted in the coupling groove 8b. In this case, the exit side end surfaces 1b of the ferrule bodies 1 are placed into contact with each other. Further, the screws thread 10b of the housing covers 10 are respectively tightly engaged with the screws thread 8c of the adapter housing 8, thus completing the connection.
At this time, a gap occurs because of a difference between the center of the small hole 1a being at the central portion of the ferrule body 1 and the center of the outer diameter of the ferrule body 1 or a difference between the inner diameter of the small hole 1a and the outer diameter of the clad of the optical fiber, whereupon an axial slippage E occurs between the center of a core portion 1d and the center of the outer diameter of the ferrule body 1 as shown in FIG. 10. Owing to this axial slippage E, if the ferrule bodies 1 are aligned with each other on the basis of their outer diameters through the use of the sleeve 9 housed in the adapter housing 8, the difference in position between the centers of the core portions 1d of the optical fibers being in opposed relation to each other comes to a maximum in the case that the slippage occurs in the opposite directions. Therefore, the positional difference F between the core portions 1d of the optical fibers being in opposed relation to each other becomes a maximum of 2E, so that the optical loss increases at the connecting point.
For eliminating this problem, in the prior art, the axial slippage E directions of the two optical connector assemblies to be joined to each other are coincided with each other with reference to the keys 4 of the optical connector housings 3 to be connected to each other, thereby minimizing the positional difference F between the core portions. In this way, the aligning work is done to reduce the optical loss at the connecting point.
In the case of the prior optical connector assemblies, after the assembling the ferrule body 1 protruding from the optical connector housing 3 can not freely rotate with respect to the key 4 of the optical connector housing 3 because the notch portions 2a made on the fixed tube base 2 are engaged with the projecting portions 3b made on the inner circumferential surface of the optical connector housing 3. Accordingly, for achieving the minimum optical loss, the key 4 of the optical connector housing 3 is made as a separate detachable part, and detached from the assembly and again attached thereto in a state where its attaching position is changed in the rotating direction. For a proper connection, this work is repeatedly done.
However, in the case of this aligning method, in addition to taking a long time, the abrasion powders of the optical connector housings and the keys generated when detaching the key sections stick to the optical fiber end surfaces of the ferrule bodies, which are cut and damaged to deteriorate their optical characteristics.
Another aligning method has been as follows.
The exit side end surface 1b of the ferrule body 1 for fixing the tube base 2 is polished before being built in the optical connector housing 3. The sleeve 9 is used without being accommodated in the adapter housing 8, and the ferrule bodies being in the opposed relation to each other are connected to each other, and they are rotated while measuring the optical loss, thereby taking the optimal position. In addition, they are inserted into the optical connector housing 3 in a state with keeping this condition, and the spring 5 is inserted thereinto and then the optical connector housing 3 is sealed with the holder 6. The alignment is accomplished by this method.
However, according to this aligning method, since the ferrule body is directly inserted into the sleeve not accommodated in the adapter housing, difficulty is encountered to straightly apply the pressing force in the direction of the axis of the ferrule body. For this reason, the sleeve receives a bending force and, hence, deforms, which produces a positional difference between the center positions of the fibers being in an opposed condition. This causes difficulty of sure alignment.
In addition, for the production of connectors with optical fibers laid for optical connector connections, it is necessary that the abrasion, alignment and assembling of optical connectors are done at the laying place or that the ferrule body sections of the optical connectors polished at a factory or the like are conveyed in a state of being not built in the spring, the optical connector housings and holders and the assembling and alignment are made at the laying place.